1. Field of the Invention
The present invention relates generally to a wireless communication system, and in particular, to a transport control method for increasing throughput of a wireless communication system through an interoperation between a medium access control (MAC) layer and a transport layer.
2. Description of the Related Art
A transmission control protocol (TCP) is designed to guarantee reliable data transmission in a wired Internet network. However, when the TCP is applied to a wireless network, throughput as in the wired network cannot be expected due to a burst error characteristic of a wireless link.
Since this burst error characteristic is similarly applied to an acknowledgement (ACK) message transmitted by a receiver to a transmitter responsive to a received packet, when an upper layer application requiring the same reliability as that of a file transmission control protocol (FTP) is served, a congestion control mechanism based on retransmission according to an ACK delay is frequently operated in the TCP. The frequent operation of the congestion control mechanism causes an increase in the number of packet retransmissions, thereby degrading system throughput.
An indirect TCP mechanism has been suggested to solve this problem. In the indirect TCP mechanism, flow and congestion control functions in a wireless link and a wired link can be separated by discriminating wireless TCP connection from wired TCP connection. However, the principal purpose of the TCP, i.e., the guarantee of end-to-end connection, disappears.
A snooping agent TCP mechanism has been suggested as an alternative for realizing the TCP in a wireless link. In the snooping agent TCP mechanism, a snooping agent is installed in a remote node and buffers a segment transmitted to a wireless terminal through a downstream link. If an ACK is not received, the snooping agent retransmits the segment to the wireless terminal. In the case of an upstream link, the snooping agent examines a sequence number of a segment received from the wireless terminal and requests the wireless terminal for retransmission of a segment of which transmission has failed using a selective repeat request algorithm. However, in the snooping agent TCP mechanism, since the snooping agent must have TCP stacks for every terminal and a memory for storing segments, it is very complicated and there are many overheads to implement the snooping agent TCP mechanism.